Ghost particles on the scales

Progress in determining neutrino mass: Research group lead by Christoph Düllmann provides exotic samples for experiments

The PENTATRAP precision mass spectrometry experiment at the Max Planck Institute for Nuclear Physics in Heidelberg (© Max Planck Institute for Nuclear Physics)

Used samples: (photo/©: Christoph Schweiger, Max Planck Institute for Nuclear Physics).

What is the mass of a neutrino at rest? A team led by the department of Professor Klaus Blaum, Director at the Max Planck Institute for Nuclear Physics in Heidelberg, with the participation of Professor Christoph Düllmann's working group at Johannes Gutenberg University Mainz (JGU), GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, and the Helmholtz Institute Mainz has now made an important contribution to the "weighing" of neutrinos as part of the international ECHo collaboration. Using the Pentratrap ion trap, the researchers have achieved an extremely precise measurement of the change in mass of the holmium-163 ion when its nucleus captures an electron and becomes dysprosium-163. From this, the researchers were able to determine this so-called Q value 50 times more accurately than before. With the help of a more precise Q-value, possible systematic errors in the determination of the neutrino mass can be uncovered.


Holmium-163 is an artificial isotope that can be produced by irradiation natural erbium-162 with neutrons, which leads to erbium-163, which in turn decays into holmium-163. The chemical isolation of the produced holmium-163 was carried out at JGU, where the sample tailored to fit the requirements of the Pentatrap experiment in Heidelberg was also produced. Pentatrap consists of five so-called Penning traps. In these traps, electrically charged atoms can be trapped for long times in a combination of a static electric and magnetic field. These ions perform an intricate "circular dance", which allows their mass to be determined with extreme precision. "With an Airbus A-380 at maximum load, you could use this sensitivity to determine whether a single drop of water has landed on it," said Christoph Schweiger, PhD student in Klaus Blaum's department at the Max Planck Institute for Nuclear Physics, illustrating the capabilities of these super scales.


C. Schweiger et al., Direct high-precision Penning-trap measurement of the Q-value of the electron capture in 163Ho for the determination of the electron neutrino mass, Nature Physics, 19 April 2024,

DOI: 10.1038/s41567-024-02461-9

Penning-trap measurement of the Q value of electron capture in 163Ho for the determination of the electron neutrino mass | Nature Physics


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Professor Dr. Christoph E. Düllmann

Department of Chemistry – TRIGA

Johannes Gutenberg University Mainz

55099 Mainz, GERMANY

phone: +49 6131 39-25852

fax: +49 6131 39-20811

e-mail: duellmann(at)


Professor Dr. Christoph E. Düllmann

Superheavy Element Chemistry

GSI Helmholtzzentrum für Schwerionenforschung

Planckstr. 1

64291 Darmstadt

phone: +49 6159 71-2462

fax: +49 6159 71-3463

e-mail: C.E.Duellmann(at)



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